1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device which has a circuit including a thin film transistor (hereinafter also referred to as a TFT) using a semiconductor film. In addition, the present invention relates to a plasma processing apparatus for a plasma CVD method used in a process for forming a thin film in manufacturing a semiconductor device. The present invention further relates to a film formation method which uses the plasma processing apparatus. For example, the present invention relates to a photoelectric conversion device typified by a solar cell or a sensor, an electro-optical device typified by a liquid crystal display panel, a light-emitting device including a light-emitting element, or an electronic device equipped with a wireless chip including an antenna as a component.
In this specification, a semiconductor device refers to all types of devices which can function by utilizing semiconductor characteristics. An electro-optical device, a light-emitting device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
In recent years, a technique for forming a thin film transistor using a semiconductor thin film (with a thickness of approximately several tens to several hundreds of nanometers) which is formed over a substrate having an insulating surface has attracted attention. A thin film transistor is widely applied to electronic devices such as an IC and an electro-optical device and has been rapidly developed particularly as a switching element for an image display device.
By a plasma CVD method, which is a typical film formation method, for example, an amorphous semiconductor film, a polycrystalline semiconductor film, a microcrystalline semiconductor film, and the like are deposited.
As a switching element for an image display device, a thin film transistor using an amorphous semiconductor film or a thin film transistor using a polycrystalline semiconductor film is known. As a method for forming a polycrystalline semiconductor film over a glass substrate, there is known a technique in which a pulsed excimer laser beam is shaped into a linear laser beam by an optical system and an amorphous silicon film formed over a glass substrate is crystallized by being scanned and irradiated with the linear laser beam.
Also, as a switching element for an image display device, a thin film transistor using a microcrystalline semiconductor film is known (Reference 1: Japanese Published Patent Application No. H4-242724 and Reference 2: Japanese Published Patent Application No. 2005-49832).
So far, a production technique by which one mother glass substrate is cut into separate sections to obtain a plurality of panels so that mass production can be efficiently performed has been employed. The size of the mother glass substrate has increased from 300 mm×400 mm for the first generation in the beginning of 1990s to 680 mm×880 mm or 730 mm×920 mm for the fourth generation in 2000s. The production technique has progressed so that a number of display panels can be obtained from one substrate.
Further, as the substrate size has been increased as described above, demands on improvement in productivity and reduction in cost have been increased.
As a TFT structure which satisfies these demands, an inverted-staggered (bottom-gate) TFT structure has been mainstream.
In addition, in accordance with miniaturization of a semiconductor element, individual processes are required to be highly precise. In a semiconductor manufacturing process, a reaction-product film which is formed by reaction of a source gas by various methods (plasma, heat, light, or the like) is deposited over a substrate to be processed which is disposed in a chamber of a film formation apparatus. In particular, suppression of particles generated in the film formation apparatus is an important objective, and keeping the inside of the chamber clean is also critical to stabilize the process.
Reference 3 (Japanese Published Patent Application No. H7-122621) discloses a substrate processing apparatus in which a plurality of treatments such as formation of a thin film over a substrate are successively performed while keeping airtightness.